docs: def DefaultSelector():
      """ This function serves as a first call for DefaultSelector to
      detect if the select module is being monkey-patched incorrectly
      by eventlet, greenlet, and preserve proper behavior. """
      global _DEFAULT_SELECTOR
      if _DEFAULT_SELECTOR is None:
          if _can_allocate('kqueue'):
              _DEFAULT_SELECTOR = KqueueSelector
          elif _can_allocate('epoll'):
              _DEFAULT_SELECTOR = EpollSelector
          elif _can_allocate('poll'):
              _DEFAULT_SELECTOR = PollSelector
          elif hasattr(select, 'select'):
              _DEFAULT_SELECTOR = SelectSelector
          else:  # Platform-specific: AppEngine
              raise ValueError('Platform does not have a selector')
      return _DEFAULT_SELECTOR()